1. Field of the Invention
This invention relates to solar heat collectors, and more particularly, to an elongated solar heat collector constructed so as to reduce heat losses therefrom and withstand internal temperatures of about 400.degree. F.
2. Description of the Prior Art
Due to the heightened energy crisis in recent years, development of alternative energy sources in lieu of increased exploitation of rapidly depleting hydrocarbon reserves has become imperative. One such alternative source is solar energy. A myriad of solar energy collector devices have been developed in the prior art for collecting and utilizing radiant energy incident on the earth's surface. A significant number of these devices are plate collectors consisting of an absorber member, a cover glazing and an insulated frame which serves as a supporting structure for the absorber member and its associated heat exchanger, and the frame for maintaining the glazing cover above the absorber plate. However, several serious problems still hamper widespread technical and commercial acceptance and success of current solar energy collectors.
One problem is the relatively large weight of the metal frame and glass cover glazing utilized in constructing conventional collectors (approximately 6 to 9 pounds per square foot). High costs are incurred in transporting and installing these heavy collectors. Often, it becomes necessary to reinforce the roof rafters or wall studs of a structure to provide support for these solar collectors. Moreover, the square or box-like peripheral configuration of these conventional collectors cannot be readily mass produced by fabrication techniques utilizing high production machinery nor be conveniently scaled up to a large area collector so as to suffice the heating requirements of a diverse range of buildings. Further, many prior art solar collectors are fabricated in relatively small modules due to the size restrictions of commercially available glass utilized as cover glazings. Thus, conventional collectors are limited to modules having lengths of 6 to 8 feet and widths of 3 to 4 feet. As a result, the high cost of conventional solar collectors is due in part to the large number of on-site piping or ducting connections necessary to establish fluid communication between modules covering the required collector area. Also, these installed arrays of conventional collectors are plagued with a relatively large heat loss since the perimeter to collector area ratio is extremely high for an array.
The relatively low thermal stability of the plastic insulation utilized is another problem posed by many state of the art solar collectors. Most insulation employed in such collectors can withstand temperatures approximating 300.degree. F. However, these collectors cannot pass stagnation tests (i.e., tests simulating pump or power failures) required by the U.S. Government prior to marketing the collector. During these certifying tests temperatures approach or exceed 400.degree. F. At such temperatures, thermal degradation of the plastic insulation occurs causing the insulation to embrittle thereby losing strength and insulating qualities. In addition, thermal degradation of the insulation will generate relatively small molecular weight volatile compounds which will condense out on cooler surfaces, such as cover glazings, resulting in fogging thereof and reducing the thermal efficiency of the collector. While measures, such as thermostatic temperature control or heat dump panels, can be taken to ensure thermal stability of prior art insulation, the attendant cost and loss of thermal efficiency of the collector render such measures undesirable.
Specifically, the following are representative examples of prior art modular solar collectors. U.S. Pat. No. 3,980,071 issued Sept. 14, 1976 to Barber discloses arrangement solar heat collector modules in a columnar and row array with the column being connected in series with appropriate headers therebetween. U.S. Pat. No. 3,937,208 issued Feb. 10, 1976 to Katz discloses a solar collection system wherein at least one solar collector is positioned on opposite sides of a collector mounting member. A flexible conduit is provided for coupling the header of one collector to the header of another collector, and in a preferred embodiment, the flexible conduit is equipped with quick-release clamps for rapid interconnection with headers of different solar collectors. U.S. Pat. No. 4,073,283 issued Feb. 14, 1978 to Lof relates to a large area solar collector system formed by a plurality of modular collector units arranged in side-by-side and end-to-end relationships and communicating by aligned passageways for transfer of fluids, such as air. U.S. Pat. No. 4,038,976 issued Aug. 2, 1977 to Stout, et al discloses a plurality of solar panels mounted on a pitched roof, each extending from the peak of the roof to the eaves thereof. These panels are fluidly connected in parallel. U.S. Pat. No. 4,055,163 issued Oct. 25, 1977 to Costello et al discloses that a plurality of solar panels may be connected together in parallel, side-by-side fashion. U.S. Pat. No. 3,939,818 issued Feb. 24, 1976 to Hamilton, et al also discloses positioning a plurality of solar heating modules in side-by-side relationship to form an array having a common intake manifold. All of these prior art arrays require extensive on-site installation labor, possess interior collectors which are relatively inaccessible for maintenance or repairs and have unncessary side walls which cast shadows on adjacent collectors. None of these patents recognize the need for an integral solar collector base having a plurality of segmented cover glazings and absorber plates for alleviating and, in some instances, eliminating these problems.
Several other prior art approaches have utilized arrays of module solar collectors having some segmentized elements. U.S. Pat. No. 4,062,351 issued Dec. 13, 1977 to Hastwell discloses modular panels which can be placed side-by-side in parallel or series flow connected together by suitably positioned openings therein. Juxtaposed panels may be placed into a common covering which connects the respective glass coverings of the panels by means of a strip of molding. However, such an array still suffers all of the shortcomings of prior art arrays. U.S. Pat. No. 4,060,071 issued Nov. 29, 1977 to Chayet relates to a solar collector having a box-like fiberglass housing covered by two lites of double strength window glass connected by a mullion. However, conventional plate glass still limits the size of this collector to a preferred length and width of substantially 4 feet by 9 inches each. Thus, an extensive array of these collectors would in most instances by required to suffice the heating requirements of a structure of any appreciable size. U.S. Pat. Nos. 3,972,317 issued Aug. 3, 1976 and 4,011,856 issued Mar. 15, 1977 disclose solar heaters in which a plurality of absorber panels are placed in side-by-side relationship within a suitable housing and are separated by fluid conduits. Typical assemblies are dimensioned 4 feet by 8 feet. Again, the solar heaters proposed by Gallagher would have to be arranged in a typical prior art array to provide for a suitable collector area.
With respect to the insulation provided within solar collectors, the prior art assemblies fail to recognize the need for insulation which can withstand temperatures of about 400.degree. F. without any attendant thermal degradation. U.S. Pat. Nos. 4,051,833 issued Oct. 4, 1977 to Vandament and 4,033,327 issued July 5, 1977 to Pei disclose polyurethane to be a suitable thermal insulating material for solar collectors. U.S. Pat. No. 4,015,582 issued Apr. 5, 1977 to Liu, et al further discloses polystyrene foam to be suitable insulating material. Such materials are thermally stable up to about 250.degree. F. for polystyrene foam and up to about 300.degree. F. for polyurethane. U.S. Pat. No. 4,033,325 issued July 5, 1977 to Walker discloses the use of isocyanurate foam as thermal insulation for a solar collector. However, isocyanurate foams possess a maximum service temperature of approximately 300.degree. F. To reiterate, none of the prior are solar collectors utilize insulation possessing thermal stability at temperatures of about 400.degree. F. nor is the need therefore recognized by the skilled artisan.
Both U.S. Pat. Nos. 3,995,613 issued Dec. 7, 1976 to Patil and 3,999,536 issued Dec. 28, 1976 to Bauer, et al disclose utilizing a moisture-impervious adhesive to bond a layer of thermal insulating material to an absorber surface. Again, there is no recognition of providing an insulative system having thermal stability at about 400.degree. F. Further, both U.S. Pat. Nos. 4,022,556 issued May 17, 1977 to Sarazin, et al and 4,026,268 issued May 31, 1977 to Bartos, et al disclose solar collectors provided with metallic foil bonded to plastic laminate and adhered to foam insulation, respectively. Again, neither patent recognizes the requirement for thermal stability of the insulating member at relatively high temperatures. Thus, a need exists to develop a solar collector which is unitary in construction for ease of installation, yet consists of certain segmented elements thereby facilitating maintenance and/or repair. An additional need exists for providing thermal insulation for solar collectors having thermal stability at about 400.degree. F.
Accordingly, it is an object of the present invention to provide a solar collector which has a unitary base and segmented absorber plates and covers.
It is also an object of the present invention to provide a lightweight, low cost solar collector which covers a relatively large collector area and which may be easily transported as assembled to the roof of a structure.
It is further object of the present invention to provide insulation for a solar collector which does not thermally degrade at temperatures of approximately 400.degree. F.
These and other objects and advantages of the invention will be apparent from the following detailed description and drawing.